Lubricant compositions containing thiopyrones



United States Patent LUBRICANT COMPOSITIONS CONTAINING THIOPYRONES ClydeS. Scanley, Stamford, Conn, and Ellis K. Fields, Chicago, 111.,assignors to Standard Oil Company, Chlcago, 11]., a corporation ofIndiana No Drawing. Application January 11, 1955 Serial No. 481,267

9 Claims. (Cl. 252-48.2)

This invention relates to oil soluble 2,6-polythio-1,4-

thiopyrones which impart resistance to oxidative deterioration whenincorporated in lubricating oil compositions.

Many of the more successful oxidation inhibitors for lubricating oil usecontain elements or chemical groups which are essential in contributingprotection for the lubricant against oxidative deterioration but whichcontribute corrosive'properties to the lubricant against certain metals.Thus, a useful and highly active bearing corrosion inhibitor issulfurized dipentene. Because of its sulfur content in active form,however, sulfiurized dipentene may be corrosive to silver or copperbearing surfaces under some conditions of use. Since this isdisadvantageous in some types of service, particularly for use as adiesel lubricant, alternative bearing corrosion inhibitors ofsatisfactory activity without corrosive properties towards silver aredesired.

We have discovered that 2,6-polythio-1,4-thiopyrones have value asinhibitors against oxidative corrosion When incorporated in lubricantcompositions. They have particular value as bearing corrosion inhibitorsand, because they are non-corrosive to silver in lubricant compositions,have a wide range of applicability. They also have value as extremepressure lubricating additives. The thiopyrones of our invention arecharacterized by the presence of disulfide or polysulfide organic groupsin the 2,6-position of the thiopyrone ring structure, and containsufficient carbon and hydrogen in the form of alkyl or hydrocarbonsubstituted alkyl groups to provide oil solubility. They are believed tohave the following structural formula:

In the formula, R and R may be hydrogen, alkyl, aryl, aralkyl, orsubstituted modifications thereof. R and R represent replacement orpartial replacement of hydrogen by hydrocarbon groups, particularly ofthe type impart ing oil solubility such as alkyl groups and substitutedalkyl groups such as naphthene and aromatic substituted alkyl groups.The subnomials x and y represent integers of two or more.

The polythio-thiopyrones are produced from 2,6-dimercapto thiopyrones,advantageously by reaction with a sulfenyl halide. The 2,6-dimercaptothiopyrones are readily produced by reaction of ketones with carbondisulfide in the presence of a strong alkali such as potash or causticsoda. The ketone may be any aliphatic or substituted aliphatic ketonehaving four active hydrogens on the a and a carbon atoms. For example,acetone, methyl ethyl ketone, benzyl ketone are convenient startingketones whereas acetophenone or benzophenone are not suitable.Substituted ketones may be used, provided that for use as lubricatingoil additives they do not introduce functional substituents which areincompatible with or unsuited to the lubricant formulation. An exampleof available substituted ketones of value are the esters of acetonedicarboxylic acid, e.g., the ethyl esters, which are readily derivedfrom citric acid.

The 2,6-dimercapto thiopyrones are converted readily to thepolythio-thiopyrones of the invention by reaction with a sulfenylhalide. The reaction may be conducted, for example, in an organicmedium, e. g., carbon tetrar chloride, at a temperature of about 0 to 10C. The sullfenyl halide, usually the chloride for convenience, isselected with a view to imparting the desired oil solubility to thefinished inhibitor. For this reason, aliphatic sulfenyl chlorides havingchain lengths of four carbon atoms or more are preferred, for example,n-butyl, t-octyl, dodecyl and the like. The aliphatic grouping, however,may comprise a substituted aliphatic such as naphthenic or aromaticsubstituted aliphatic chains as in 3-cyelohexylpropylsulfenyl chlorideor benzyl sulfenyl chloride. These sulfenyl chlorides are readilyderived from the corresponding mercaptans by chlorination. Thepolythio-thiopyrones also may be produced from 2,6- dimercaptothiopyrone by reaction with a mercaptan and sulfur or by reaction with amercaptan and a sulfur halide such as sulfur monochloride.

The new products are viscous liquids of varying oil solubility dependingupon the amount and nature of hydrocarbon substitution in the structureand the nature of the base oil. In general, it is desirable that thepolythiothiopyrones contain eight or more carbon atoms in the form ofaliphatic substituents in order to provide adequate oil solubility.Thus, it is usually desirable in preparation to employ an alkyl orsubstituted alkyl sulfenyl halide providing at least 4 carbon atoms inthe alkyl chain and to react the dimercapto thiopyrone intermediate withthe stoichiometric proportion, or a slight excess, of a sulfenyl halide.can be selected as starting materials in the preparation of thedimercapto thiopyrone intermediate. The products then can be handled inthe form of mineral oil concentrates which facilitate handling in theformulation of commercial lubricating oils and greases. The level of usein the finished lubricants, however, is usually quite small. For use asan oxidation inhibitor in a hydrocarbon oil susceptible to oxidativedeterioration the concentration of the additive may be in the range ofabout 0.001 to 1 percent by weight. For use as a bearing corrosioninhibitor in crank case lubrication, the inhibitor is used in the rangeof about 0.005 to 5 percent by weight. For use as an additive to impartextreme pressure lubricating properties to mineral oil lubricants, theadditive is used in the range of from about 0.1 to about 10 percent byweight.

In commercial formulation, the polythio-thiopyrone additives willordinarily be used, as is customary in conjunction with other,compatible lubricating oil additives, for example, pour depressants,viscosity index improvers, anti-rust agents, anti-foam agents and thelike. The base may comprise any hydrocarbon oil subject to oxidativedeterioration. For most applications, the oil will comprise a mineraloil fraction of the usual viscous lubricating oil range.

As produced by reaction of a 2,6-dimercapto thiopyrone with a sulfenylhalide, the product is a 2,6-dithio, 1,4- thiopyrone. We have furtherfound that additional sulfur can be incorporated at the disulfidelinkage by direct sulfurization so that a variety of polysulfidederivatives can be readily prepared. The sulfurization is conducted at atemperature at about to about 200 C., by reaction of the thiopyrone withsulfur for a period ranging from a few minutes to several hours. Theresulting polysulfide derivatives in general show improved extremepressure degree of Alternatively, longer chain ketones.

inhibitors with respect to corrosive tendencies toward silver and copperbearing surfaces.

The invention will be further illustrated by means of specific examples.In the examples, the new additives were evaluated by means of a stirringsand corrosion test (SSCT) and the well known EMD silver bearingcorrosion test.

The SSCT test was run as follows: A copper-lead test specimen is lightlyabraded with steel wool, washed with naphtha, dried and Weighed to thenearest milligram. The cleaned copper-lead test specimen is suspended ina steel beaker, cleaned with a hot tri-sodium phosphate solution, rinsedwith water and acetone and dried. 250 grams of the oil to be testedtogether with 0.625 gram lead oxide and 50 grams of a 3035 mesh sand arecharged to the beaker. The beaker is then placed in a bath or heatingblock and heated to a temperature oat 300 F. (i2 F.) while the contentsare stirred by means of a stirrer rotating at 750 rpm. The contents ofthe beaker are maintained at this temperature for twentyfour hours,after which the copper-lead test specimen is removed, rinsed withnaphtha, dried and weighed. The test specimen is then replaced in thebeaker and an additional 0.375 gram of lead oxide added to the test oil.At the end of an additional twenty-four hours of test operation the testspecimen is again removed, rinsed and dried as before, and weighed. Thetest specimen is again placed in the beaker together with an additional0.250 gram of lead oxide and the test continued for another twenty-fourhours (seventy-two hours total). At the conclusion of this time, thetest specimen is removed from the beaker, rinsed in naphtha, dried andweighed. The loss in weight of the test specimen is recorded after eachweighing. A weight loss of 200 mg. or less in 48 hours and 500 mg. orless in 72 hours is allowable.

In the EMD test a silver strip 2 cm. x 5.5 cm. with a small hole at oneend for suspension is lightly abraded with No. steel wool, wiped free ofany adhering steel wool, washed with carbon tetrachloride, aindried andthen weighed to 0.1 milligram. Three hundred cc. of the oil to be testedis placed in a 500 cc. lipless glass beaker and the oil is heated to atemperature of 300 F. (12 F.) and the silver test strip suspended in theoil so that the strip is completely immersed therein. The oil in thebeaker is stirred by means of a glass stirrer operating at 300 rpm. Atthe end of twentyafour hours, the silver strip is removed and whilestill hot rinsed thoroughly with carbon tetrachloride and air-dried. Theappearance of the strip is then visually noted and given ratingsaccording to the following scale:

1-Bright 2-Stained 3Grey-black 4-Black, smooth 5-Black, flake After thevisual inspection the silver strip is immersed in a potassium cyanidesolution at room temperature until the silver surface assumes itsoriginal bright or silver appearance. The silver strip is then washedsuccessively with distilled water and acetone, air-dried and weighed. Aweight loss of 20 mg. or less is considered passing.

4 Example I 2,6-dimercapto-3 -methyl-l,4-thiopyrone was prepared frommethyl ethyl ketone, carbon disulfide and potassium hydroxide.

A carbon tetrachloride suspension of 0.0398 mole of this dimercaptan wastreated at 0 C. for three hours with 0.0796 mole of n-dodecyl sulfenylchloride (prepared by chlorinating n-dodecyl mercaptan). The reactionmixture was washed with dilute alkali and with water and then wasstripped of carbon tetrachloride by nitrogen blowing at 220 F. Theproduct was a viscous liquid containing 23.5 percent S. Theoretical forA solvent extracted SAE 30 grade Mid-Continent oil (containing about 3percent detergent) and 0.75% sulfurized dipentene gave 100 mg. silverloss in the EMD test. When 0.2 percent of the product from Example I wasadded to the above oil, the EMD silver loss was reduced to 1.7 mg. Thedeactivated oil gave SSCT losses of 23 mg. at 48 hours and 53 mg. at 72hours.

Example III Example IV 2,6-dimercapto-3,5-diphenyl-1,4-thiopyrone HS SEwas prepared from dibenzylketone, carbon disulfide and potassiumhydroxide. Nine grams of the thiopyrone Was added to the solution of.055 mole of n-hexyl sulfenyl chloride in 50 cc. of carbontetrachloride. The mixture was heated at -100 F. for /2 hour. Thereaction mixture was washed with dilute alkali and with water and thenwas stripped of carbon tetrachloride in vacuo. The crude reactionproduct is a very viscous yellow oil and contained 28.1% sulfur. Theproduct was tested at 0.75% concentration level in solvent extractedSAE-30 grade Mid-Continent oil containing about 3% Off a detergent ofthe neutralized phosphorus sulfide-polybutene reaction product type, Theoil gave a bright EMD silver strip and SSCT 'weight losses of 89milligrams at 48 hours and 123 milligrams at 72 hours.

We claim:

1. A lubricant composition which comprises a major proportion of ahydrocarbon'lubn'cating oil base and an oil soluble2,6-polythio-1,4-thiopyrone which contains at least one alkylhydrocarbon group in the 2,6 positions imparting oil solubility theretoin an amount at least suflicient to impart protection against oxidativedeterioration of the hydrocarbon base oil. I

2. A lubricant composition which comprises a major proportion of ahydrocarbon lubricating oil base and an oil soluble2,6-dithio-l,4-thiopyrone which contains at least one alkyl hydrocarbongroup in the 2,6 positions imparting oil solubility thereto in anamountat least sufficient to impart protection against oxidativedeterioration of the hydrocarbon base oil.

3. A lubricant composition which comprises a major proportion of a.hydrocarbon lubricating oil base and an oil soluble2,6-alky1-dithio-1,4-thiopyrone in an amount at least suflicient toimpart protection against oxidative deterioration of the hydrocarbonbase oil.

4. A lubricant composition which comprises a major proportion of ahydrocarbon lubricating oil base and an oil soluble 2,6alkyldithio-S-hydrocarbon substituted-1,4- thiopyrone in an amount at leastsuflicient to impart protection against oxidative deterioration of thehydrocarbon base oil.

5. A lubricant composition which comprises a major proportion of ahydrocarbon lubricating oil base and an oil soluble 2,6-a1kyldithio-3,5-hydrocarbon substituted 1,4-thiopyrone in an amount at leastsufiicient to impart protection against oxidative deterioration of thehydrocarbon base oil.

6. A lubricant composition which comprises a major proportion of ahydrocarbon lubricating oil base and a 2,6-bis-t-octyldithio-3-methyl-1,4 -thiopyrone in an amount at least sufiicient toimpart protection against oxidative deterioration of the hydrocarbonbase oil.

7. A lubricant composition which comprises a major proportion of ahydrocarbon lubricating oil base and a 2,6-bis-t-dodecyldithio-3-methyl-1,4-thiopyrone in an amount at least sufiicient toimpart protection against oxidative deterioration of the hydrocarbonbase oil.

8. A lubricant composition which comprises a major proportion of ahydrocarbon lubricating oil base and a 2,6-bis-t-oetyldithio-3,5-diphenyl-1,4-thiopyrone in an amount at least suflicient' toimpart protection against oxidative deterioration of the hydrocarbonbase oil.

9; A lubricant composition which comprises a major proportion of ahydrocarbon lubricating oil base and an oil soluble sulcfurized2,6-alkyl dithio-1,4-thiopyrone in an amount at least sufiicient toimpart protection against oxidative deterioration of the hydrocarbonbase oil.

References Cited in the file of this patent UNITED STATES PATENTS2,434,100 Bousquet Jan. 6, 1948 2,562,145 Harman et al. July 24, 19512,653,910 Airs et a1 Sept. 29, 1953 2,709,682 Knowles May 31, 1955

1. A LUBRICANT COMPOSITION WHICH COMPRISES A MAJOR PROPORTION OF AHYDROCARBON LUBRICATING OIL BASE AND AN OIL SOLUBLE2,6-POLYTHIO-1,4-THIOPYRONE WHICH CONTAINS AT LEAST ONE ALKYLHYDROCARBON GROUP IN THE 2,6 POSITIONS IMPARTING OIL SOLUBILITY THERETOIN AN AMOUNT AT LEAST SUFFICIENT TO IMPART PROTECTION AGAINST OXIDATIVEDETERIORATION OF THE HYDROCARBON BASE OIL.